An inductor is a passive electronic component that stores energy (measured in henrys (H)) in the form of a magnetic field. In its simplest form, an inductor consists of a wire loop or coil, and the inductance is directly proportional to the number of turns in the coil. Inductance also depends on factors such as the radius of the coil and the type, e.g. magnetic permeability, of material, around which the coil is wound, i.e. the core. An inductor impedes the flow of high-frequencies in an alternating current (AC) circuit, and thus may be used as surge protectors to choke off high-frequency shifts. An inductor may also be connected in series or parallel with a capacitor to provide discrimination against unwanted signals, which is advantageous for use in wireless communications applications. In addition, inductors are used in the power supplies of electronic equipment of all types, including computers and their peripherals. In these systems, simple inductors and more complex coupled inductors such as multi winding transformers, may be used in the power train of switching power converters such as in the buck, boost, buck-boost, forward, and flyback topologies and also in filters helping to smooth out rectified AC, providing pure, battery-like direct current (DC).
Inductors can be manufactured as a surface mount device (“SMD”), which is a device that is mounted directly to the surface of a PCB. For example, the inductor is placed on the surface of the PCB and then the assembly is moved through an oven in a solder reflow process. The temperatures of the oven are sufficiently high to liquefy solder placed between the inductor and the PCB, and after the PCB is removed from the oven and cools, the solder hardens to provide a mechanical and electrical connection. Conventional chip-type surface mount inductors may be rectangular, and the wire surrounding the core (the windings) may be encapsulated in a plastic or other non-conductive material. Electrically conductive terminals on one or more end portions of the surface mount inductor are exposed for connection to contacts on the PCB. Such packaged inductors consume a large amount of space on a PCB, and space considerations are of the utmost importance in consumer electronics, portable devices, and many other communication devices.
In an effort to save space and increase reliability, planar magnetic components such as inductors and transformers may be constructed using PCB manufacturing techniques, wherein the windings and individual winding turns are conductive traces patterned in one or more of the conductive layers of a multilayer PCB. The resulting assembled planar magnetic PCB inductor has a smaller mounting footprint than an inductor having a conventional winding, and the traces that form the windings have proven to be more reliable than prior art windings because the chances of shorting over adjacent turns of the winding is reduced.
An example of a power converter which uses a planar magnetic structure is described and shown in Vinciarelli, Power Converter Package and Thermal Management, U.S. Pat. No. 7,361,844 B2 (assigned to VLT, Inc., Sunnyvale, Calif. and incorporated here by reference) (the “VIC patent”). The VIC patent shows in FIGS. 5A and 5B a power converter including a PCB 442, magnetic core structures 422a, 422b, and additional power conversion circuitry in a package having an upper portion and a lower portion that respectively enclose circuitry on a top surface and a bottom surface of the circuit board. The lower portion encloses a smaller region than that of the upper portion, and the regions are arranged to define an overhang region. Interface contacts on the bottom surface in the overhang region are provided for making electrical connections to an external circuit board.
Power converters that must satisfy low voltage and high current capacity requirements can be expensive to make using planar magnetics because the windings of the inductor or transformer design may require a substantial number of PCB layers, and the overall cost of the converter using such an inductor or transformer formed in the multilayer PCB may be proportional to the number of layers and the amount of conductive material, such as copper, used in each layer, and the PCB area. For example, in order to handle a high current of over 40 amperes with a two or three turn winding with low loss, a multilayer PCB could be composed of eight to ten layers or more that may require approximately four ounces of copper. Furthermore, it is difficult to manufacture such a multilayer PCB to include both inductors and additional electrical circuitry, which further increases the cost.
In Electronic Module Structure, U.S. Pat. No. 2,786,969, Blitz discloses a composite electric component module that includes a plurality of wafer elements having flat, component-supporting surfaces, and riser members that are box-shaped with angularly extending edges. When the structure is formed the edges of one riser member are adjacent the edges of another to provide a one-piece, box-shaped module structure with the wafer elements disposed between adjacent riser members. Circuit components are carried by the supporting surfaces of the wafer elements, and electrically conductive paths are provided on these surfaces and on the inner surfaces of the riser members.
In Wafer Parametron, U.S. Pat. No. 3,087,096, Jorgensen discloses circuit components in the form of minor modules (parametrons) having elements of construction for participating in the response of an electrical circuit, and which can be assembled in groups to form a major module of a complex device. Each parametron consists of a thin wafer of dielectric material for supporting a printed circuit, the wafer having input tabs formed on a first edge and output tabs formed on another, separate edge. The wafer also supports a ferrite core mounted in a perforation, wherein the windings of the core are appropriately connected to traces of the printed circuit. A described embodiment is a triangular construction consisting of an array of three parametrons, wherein the three parametrons are arranged to form a triangular base. This configuration of parametrons can be utilized as a plug in module, for example, for use as a component of a digital computer.
In Surface Mount Inductor, U.S. Published Patent Application No. 2007/0285200, Hsieh discloses a structure for a surface mount inductor having a decreased height when compared to the prior art. The structure consists of two erected side panels and a central part coupled therebetween forming an H-shaped core. A wire is wound around the central part, two terminals are coupled to the conductor contacts of the core, and a casing forming a chamber is provided for receiving the core.
In Vertical Surface Mount Assembly and Methods, U.S. Pat. No. 6,087,723, Kinsman et al. disclose a vertically mountable semiconductor device assembly that includes a semiconductor device and a mechanism for attaching the semiconductor device to a carrier substrate. In particular, the vertically mountable semiconductor device includes bond pads disposed proximate an edge. The assembly also includes a retainer that engages the semiconductor device, and an alignment device that is attached to a carrier substrate. The alignment device secures the vertically mountable semiconductor device package in an orientation that is perpendicular to the plane of the carrier substrate.
State of the art microprocessors and memory are increasingly faster and smaller in size, and require small footprint components that can deliver low voltages at increasingly higher currents. Thus, there is a need for an improved, cost effective, small footprint inductor module for use with power converter circuitry. Such a device should also be compatible with existing PCB surface mounting techniques and be less expensive than prior art devices.